DC offset cancelling circuit applied in a variable gain amplifier

Abstract

The present invention discloses a DC offset canceling circuit applied in a variable gain amplifier. The DC offset canceling circuit comprises a transconductance amplifier and at least one internal capacitor to function as a filter. The input of the transconductance amplifier is electrically connected to the output of the variable gain amplifier, and the output of the transconductance amplifier and the at least one internal capacitor are electrically connected to the input of the variable gain amplifier to form a feedback loop. To cooperate with the function of the DC offset cancelation, the input stage of the variable gain amplifier comprises an auxiliary differential pair.

What is claimed is:  
     
       1. A DC offset canceling circuit applied in a variable gain amplifier, comprising: 
       a transconductance amplifier electrically connected to the output of the variable gain amplifier for transforming an input voltage to an output current based on a ratio;  
       at least one internal capacitor electrically connected to the output of said transconductance amplifier for generating a low-pass filtering function by working together with said transconductance amplifier; and  
       an auxiliary differential pair situated at the input of said variable gain amplifier and electrically connected to the output of said transconductance amplifier.  
     
     
       2. The DC offset canceling circuit applied in a variable gain amplifier of  claim 1 , wherein said variable gain amplifier comprises a first amplifier as an input stage, and said auxiliary differential pair is embedded in the input stage of said first amplifier. 
     
     
       3. The DC offset canceling circuit applied in a variable gain amplifier of  claim 1 , wherein said transconductance amplifier and said at least one internal capacitor are embedded in a chip.